Field of the Invention
The present invention relates to metal effect pigments comprising a metallic substrate in platelet form and a coating applied thereto, wherein the coating comprises at least one spacer layer, and to a process for production of the metal effect pigments and to the use thereof.
Description of Related Art
EP 1 270 682 A2 discloses multilayer luster pigments based on a metallic substrate. The luster pigments comprise a plurality of layers composed of (A) at least one layer stack consisting of i) a colorless dielectric layer composed of a material having a refractive index n≤1.8 and ii) a colorless dielectric layer composed of a material having a refractive index n>1.8, and (B) a selectively or nonselectively absorbent layer. EP 1 270 682 A2 does not give any pointer to a spacer layer within the coating.
EP 1 114 103 A1 discloses multilayer pigments based on metal pigments in platelet form, wherein the metal pigments have been coated with an amorphous vitreous layer and subsequently with one or more metal oxides or metal oxide mixtures. There is no description of a spacer layer within the coating in EP 1 114 103 A1.
EP 1 685 198 A2 discloses effect pigments having an aluminum or aluminum alloy core in platelet form and an aluminum oxide- or aluminum oxide/hydroxide-containing layer that surrounds the aluminum or aluminum alloy core and is obtainable by wet-chemical oxidation of the core. The effect pigments have been coated with at least one metal chalcogenide layer of high refractive index, with formation of a mixed layer owing to the porosity of the aluminum oxide- or aluminum oxide/hydroxide-containing layer between the metal chalcogenide layer of high refractive index and the surrounding aluminum oxide- or aluminum oxide/hydroxide-containing layer. The pores that form in the aluminum oxide- or aluminum oxide/hydroxide-containing layer as a result of the wet-chemical oxidation of the core are not arranged essentially parallel to the surface of the aluminum or aluminum alloy core, but distributed randomly in the aluminum oxide- or aluminum oxide/hydroxide-containing layer.
EP 0 708 154 A2 discloses luster pigments based on multiply coated metallic substrates in platelet form, which have at least one layer stack composed of A) a colorless coating having a refractive index of n≤1.8 and B) a selectively absorbent coating with a refractive index n≥2.0 and, if desired, additionally C) an outer colorless or selectively absorbent coating different than the layer B) beneath. EP 0 708 154 A2 does not disclose a spacer layer within the coating.
EP 0 668 329 A2 discloses luster pigments based on multiply coated metallic substrates in platelet form comprising A) a first layer consisting essentially of silicon oxide, silicon oxide hydrate, aluminum oxide and/or aluminum oxide hydrate, B) a second layer consisting essentially of metal and/or nonselectively absorbent metal oxide, and C) if desired a third layer consisting essentially of colorless or selectively absorbent metal oxide. EP 0 668 329 A2 does not contain any pointer to a spacer layer within the coating.